1. Field of the Invention
The present invention relates to a device for holding an optical disk around a rotary shaft of a motor and, more particularly, to such a device in which a plurality of spring-loaded radial tongues are shaped in such a manner that the tongues may make contact with the rounded inner edge of the optical disk at a full contact length in spite of the thickness of the disk.
2. Description of Related Art
As shown in FIG. 1, a device 10 in prior art for holding an optical disk 2 around a rotary shaft (not shown) of a motor 1 includes a casing 11 having a plurality of equispaced openings 12 formed around, and a plurality of spring-loaded radial tongues 13 partially extended out from the openings 12.
These spring-loaded radial tongues 13, retractable into the openings 12, are provided for engaging with an rounded inner edge 20 of the optical disk 2 to hold and rotate the same disk 2.
Referring to FIGS. 2 and 3, each radial tongue 13 has an upper curved surface 131 and a lower curved surface 132, over which the rounded inner edge 20 of the optical disk 2 may slide to retract the tongue 13. When the disk 2 is held in place around the rotary shaft, the spring-loaded tongues 13 are extended out again until their lower curved surfaces 132 make contact with the rounded inner edge 20 of the disk 2. With such a contact, the optical disk 2 can be rotated by the tongues 13 synchronously with the rotation of the motor 1, as shown in FIG. 1.
In the prior art device 10, however, the lower curved surface 132 of each tongue 13 is curved differently from the rounded inner edge 20 of the optical disk 2. As can be clearly seen in FIGS. 2 and 3, they make contact with each other only at two points 21a and 21b, with an intervening clearance 21 remaining between the lower curved surface 132 and the rounded inner edge 20 of the disk 2.
The point contact is more disadvantageous to any optical disk 2 which is thinner than usual. This is because the spring-loaded tongue 13 is extended radially outward a little further and thus exerts a weaker force upon the disk 2. The reduced force at the contact points 21a and 21b impairs the ability of the tongues 13 to hold the disk 2 securely in place, and so the thinner disk 2 may slightly slide relative to the device 10 and rotates at a mismatched speed slower than that of the rotary shaft of the motor 1.